Use this article to see the universe of options.
Use multiple displays with your Mac - Apple Support
The section on Mirroring is excessively upbeat. Mirroring forces a compromise resolution that too often fails or is less than acceptable for one display or the other. I suggest you turn Mirroring OFF. Using the Arrange pane, drag the MenuBar Icon to the external display to make it the Primary display.
Regardless or the capabilities of your HDMI display, you are (practically speaking) limited to 1920 by 1080p, unless you take extraordinary measures to make absolutely every setting and every adapter and every cable provide support for wider than 1920 wide. if you do all that, then in some cases you may get access to wider screens, often at 30-Hz refresh.